To conclude, logical positivism was progressive compared with the classical positivism of Ptolemy, Hume, d'Alembert, Compte, John Stuart Mill, and Ernst Mach. It was even more so by comparison with its contemporary rivals—neo-Thomisism, neo-Kantianism, intuitionism, dialectical materialism, phenomenology, and existentialism. However, neo-positivism failed dismally to give a faithful account of science, whether natural or social. It failed because it remained anchored to sense-data and to a phenomenalist metaphysics, overrated the power of induction and underrated that of hypothesis, and denounced realism and materialism as metaphysical nonsense. Although it has never been practiced consistently in the advanced natural sciences and has been criticized by many philosophers, notably Popper (1959 [1935], 1963), logical positivism remains the tacit philosophy of many scientists. Regrettably, the anti-positivism fashionable in the metatheory of social science is often nothing but an excuse for sloppiness and wild speculation.

Hayek thought there are two orders through which individuals consider the world: the sensory order and the physical order. The sensory order is what we sense. The physical world is the real world of existence beyond our senses that every sane person who is not a solipsist accepts on faith. According to Hayek, advances in science have rendered any correspondence between the real, physical world and the sensory world almost nonexistent. Instead, the natural, real world expresses itself in mathematical relationships.Hayek’s views tended philosophically to solipsism. While he believed in the existence of a physical world external to mind, he ascribed almost no (if any) properties to it.He was not as opposed to positivism as to logical positivism, and it is important to be clear about these terms. Positivism is simply the idea that there should be some correspondence with the material world extrinsic to one’s physical self that one perceives in order for statements about nature to be valid, to be true. Using this broad definition of positivism, Hayek was a positivist. Logical positivism tries to go a step beyond this position. The logical positivists sought to reduce all experience to sensory experience and to reduce every sensory experience to a conclusive or exact statement. This has proven an unattainable goal.

:...Vienna is the origin of so many schools of its own which were dominant in the 1920s. And one of the most fundamental and influential, in which we all were partially caught, was logical positivism. In fact, Mises’ brother, Richard von Mises, became one of the leading figures. Now he and I all grew up in this Ernst Mach philosophy that ultimately everything must be rationally justified…

Logical positivism is a very attractive view for people who do not want to worry about what they cannot observe. It is ultimately a theory about meaning, about the content of a theory. According to the positivists, a theory says no more than its observable consequences.Logical positivism has been killed many times over by philosophers. But no matter how many stakes are driven through its heart, it arises unbidden in the minds of scientists. For if the content of a theory goes beyond what you can observe, then you can never, in principle, be sure that any theory is right. And that means there can be interminable arguments about which theory is right that cannot be settled by observation.